I have a mewtwo and it has a modest nature, perfect IVs, and max EVs in sp attack and speed. the remaining 4 go to HP. the moveset is thunderbolt, flamethrower, ice beam, and aura sphere. held item is a life orb. is this good?

Yes, though some could argue that Flamethrower is quite useful against pokemons such as Scizor in Ubers. Sure, it's not common, but Mewtwo isn't one to take a Banded Bullet Punch easily, especially after Hazard damage and LO Recoil.